The problem most people ignore is that train marginal-increases max-out at some number of trains per day, before you need an additional set of tracks.
And that happens at a much lower number than most people assume, especially if you're planning on sharing that track with other routes. And even worse if you have to use or cross a freight track.
So not only does efficiency have a min bounds, but also a local-max bounds, where you need a large enough marginal increase to justify the additional rails.
Whereas the airline equivalent is whether to schedule an additional flight. Which is easier to commit to than whether a new track is justified.
Multi-track railways are common near major cities. They are not that expensive, because adding another set of tracks increases the width of the corridor only marginally.
The airline equivalent of a new set of tracks is building a new runway. Because that's often impossible, landing slots at busy airports have become very valuable. For example, airlines have paid tens of millions for a daily landing slot at Heathrow.
About a quarter of all railway passengers in Czechia take the suburban trains around Prague.
We sorely need extra sets of tracks from all directions, because the current tracks are overloaded. Especially the faster trains from other regions do not mix well with the regional trains that stop every 2 km or so.
But it is almost impossible to build those extra sets of tracks in a densely populated major city like Prague. Lots of NIMBYs, the needed land would be very expensive, many buildings would have to be torn down, plus the centre is a protected zone (historical buildings) and the protecting authorities fight tooth and nail against anything that changes the look and feel of the inner city.
As a result, we are stuck with old infrastructure even if new one is sorely needed. There might be a way, namely, to build all the new tracks underground - but that would be very, very expensive.
edit: By that I mean something like illustrated here https://ca.wikipedia.org/wiki/L%C3%ADnia_9_del_metro_de_Barc...
Make them 15 to 16 meters in diameter to be usable by any train, or use 2 of them side by side. Problem mostly solved.
Our subway system was rather expensive to build and maintain, doing this with trains would probably be too expensive even for a fairly rich city like Prague.
There are some rudimentary plans for railway tunnels under the very center of the city, but the expected cost is eye-watering.
We're in a phase of low interest rates, resulting in easy money politics. Burn some billions before others do ;->
Except many world's biggest airports, like Heathrow, are operating at peak capacity and building another runway at heathrow is expensive, controvertial, involves relocating people's homes and is still a political football
So it's more appropriate to compare it to part of the station cost, along the lines of another boarding area & track, increasing arrivals and departures.